Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Twisted WSe₂ as a highly tunable platform for the study of exotic phenomena


In recent years two-dimensional quantum materials have provided a platform for the realization of novel correlated and topological phases of matter. In a paper just published in Nature Materials, an international research team involving scientists from Germany, the United States, China and Japan reports that the twisted bilayer transition metal dichalcogenide WSe₂ enables the realization of exotic correlated phenomena, including high-Tc superconductivity and correlated insulators, in a controlled manner and without the geometrical restriction found in twisted bilayer graphene.

In their search for new materials which can conduct electricity without any resistance, the so-called superconductors, many scientists now investigate two-dimensional materials to advance their understanding of high-temperature superconductivity as well as other exotic materials phases.

Schematic of twisted bilayer WSe₂, where a correlated insulator phase and a possible superconducting transition emerge at a relatively wide range of small twist angles.

Jörg Harms / MPSD

These ultra-thin substances, only one atom layer thick, can develop surprising new characteristics when they are laid on top of one another.

This means that scientists can engineer new properties in such materials by stacking thin layers in a particular, controllable fashion. One of the simplest and most interesting ways is to place two layers of the same material on top of each other with a slight twist.

Depending on the angle of this twist, the layering causes significant changes in the material's electronic properties. Graphene, for example, can develop superconducting characteristics at a surprisingly high temperature when its 2D layers are twisted – a property it does not possess in its normal state.

Previous studies have shown that when two layers of graphene are stacked on top of each other with a slight twist (‘twisted bilayer graphene’), the low-energy electronic states are strongly localized and the kinetic energy scale of those states is significantly quenched.

As a result, electron-electron correlations become important, so that with slight doping, the system is driven into Mott-like insulator and superconductor phases, with a phase diagram resembling those of high Tc superconductors. Therefore, twisted bilayer graphene is a novel platform for the study of exotic correlated phenomena, including high Tc superconductivity. Its simple structure and easy accessibility make it a promising material for research in this field.

However, twisted bilayer graphene also has its limitations. Due to its special electronic structure, the strong suppression of the kinetic energy scale only happens at specific twists – the so-called magic angles (starting at around 1.1°). Thus, the fascinating strongly correlated phenomena described above are only observed very close to the magic angle. This poses a challenge to the experimental realization in real laboratory conditions and also limits the tunability of the study.

Now, the international research team with scientists from the Max Planck Institute for the Structure and Dynamics of Matter (MPSD), RWTH Aachen University (both in Germany), Columbia University, the Center for Computational Quantum Physics at the Flatiron Institute (both in the USA), Nanjing University in China and the National Institute for Materials Science in Japan focused on shedding new light on the properties of those novel atomically thin materials.

They report that similar phenomena can appear in the twisted bilayer transition metal dichalcogenide WSe₂, but – crucially – without the strict constraints imposed by any magic angles.

The team measured the transport properties of twisted bilayer WSe₂ at low temperatures with varying external magnetic fields and displacement fields. They found the signatures of the correlated insulator phases in samples with twist angles ranging from 4° to 5.1°.

These correlated phases are highly tunable with twist angles and external displacement fields, which can be rationalized in terms of an effective Hubbard model on a two-dimensional triangular lattice.

In the sample with a twist angle of 5.1°, zero-resistance pockets are observed near the correlated insulator phase at a temperature below 3K, indicating a possible transition to a superconducting state. These new findings by Cory Dean’s and Abhay Pasupathy’s experimental groups at Columbia University were explained through extensive first principles and model calculations by Lede Xian and Ángel Rubio in the MPSD’s Theory Department, Martin Claassen at the Simons Foundation's Flatiron Institute and Dante Kennes at the RWTH Aachen University.

This study establishes that the twisted bilayer transition metal dichalcogenide WSe₂ is a highly tunable platform to engineer electronic band structures. It permits the detailed study of strongly correlated phenomena which would otherwise remain inaccessible, with great experimental and theoretical potential. In particular, the system provides a unique tunable solid-state realization of a single band Hubbard model on a triangular system where bandwidth and doping can be independently varied.

“Hence WSe₂ represents a promising alternative material for research into superconductivity and other exotic phenomena, such as exciton condensates, spin liquids, and magnetic ordering”, explains the director of the MPSD’s Theory Department, Ángel Rubio. “It opens up new opportunities for studying the interplay between strong interactions and frustration.”

Wissenschaftliche Ansprechpartner:

Lede Xian (MPSD author):
Jenny Witt (MPSD PR and Communications):


Weitere Informationen:

Jenny Witt | Max-Planck-Institut für Struktur und Dynamik der Materie

More articles from Materials Sciences:

nachricht Goodbye Absorbers: High-Precision Laser Welding of Plastics
10.07.2020 | Fraunhofer-Institut für Lasertechnik ILT

nachricht Shock-dissipating fractal cubes could forge high-tech armor
08.07.2020 | DOE/Los Alamos National Laboratory

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: The spin state story: Observation of the quantum spin liquid state in novel material

New insight into the spin behavior in an exotic state of matter puts us closer to next-generation spintronic devices

Aside from the deep understanding of the natural world that quantum physics theory offers, scientists worldwide are working tirelessly to bring forth a...

Im Focus: Excitation of robust materials

Kiel physics team observed extremely fast electronic changes in real time in a special material class

In physics, they are currently the subject of intensive research; in electronics, they could enable completely new functions. So-called topological materials...

Im Focus: Electrons in the fast lane

Solar cells based on perovskite compounds could soon make electricity generation from sunlight even more efficient and cheaper. The laboratory efficiency of these perovskite solar cells already exceeds that of the well-known silicon solar cells. An international team led by Stefan Weber from the Max Planck Institute for Polymer Research (MPI-P) in Mainz has found microscopic structures in perovskite crystals that can guide the charge transport in the solar cell. Clever alignment of these "electron highways" could make perovskite solar cells even more powerful.

Solar cells convert sunlight into electricity. During this process, the electrons of the material inside the cell absorb the energy of the light....

Im Focus: The lightest electromagnetic shielding material in the world

Empa researchers have succeeded in applying aerogels to microelectronics: Aerogels based on cellulose nanofibers can effectively shield electromagnetic radiation over a wide frequency range – and they are unrivalled in terms of weight.

Electric motors and electronic devices generate electromagnetic fields that sometimes have to be shielded in order not to affect neighboring electronic...

Im Focus: Gentle wall contact – the right scenario for a fusion power plant

Quasi-continuous power exhaust developed as a wall-friendly method on ASDEX Upgrade

A promising operating mode for the plasma of a future power plant has been developed at the ASDEX Upgrade fusion device at Max Planck Institute for Plasma...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Contact Tracing Apps against COVID-19: German National Academy Leopoldina hosts international virtual panel discussion

07.07.2020 | Event News

International conference QuApps shows status quo of quantum technology

02.07.2020 | Event News

Dresden Nexus Conference 2020: Same Time, Virtual Format, Registration Opened

19.05.2020 | Event News

Latest News

Did nerve cells evolve to talk to microbes?

10.07.2020 | Life Sciences

Cherned up to the maximum

10.07.2020 | Physics and Astronomy

Road access for all would be costly, but not so much for the climate

10.07.2020 | Ecology, The Environment and Conservation

Science & Research
Overview of more VideoLinks >>>